3-4 Impact and risk analysis for the Galilee subregion

Executive summary

The impact and risk analysis for the Galilee subregion is a regional overview of potential impacts on, and risks to, water resources and water-dependent ecological, economic and sociocultural assets from coal resource development. Hydrological and ecosystem changes due to coal resource development are quantified where possible and impacts that are very unlikely (less than 5% chance) are ruled out.

The Galilee subregion in central Queensland encompasses the headwaters of six major river basins with almost all proposed coal resource developments situated in the headwaters of the Burdekin river basin. In most rivers, water flow is strongly seasonal and, from year to year, flows can vary greatly from almost no flow to major floods.

Results from regional-scale hydrological modelling indicates that the future development of seven large coal mines in the central-eastern Galilee Basin is very likely (greater than 95% chance) to lead to cumulative hydrological changes in regional groundwater and surface water flow systems. These changes, focused in the Belyando river basin, will affect a larger area and total length of stream network than previously predicted from any individual mine-scale impact assessments. More detailed local-scale information is required to enhance existing knowledge of the level of risk and potential impacts.

Coal resources

baseline coal resource development (baseline): a future that includes all coal mines and coal seam gas (CSG) fields that were commercially producing as of December 2012

in the Galilee subregion there are no existing coal resource developments and so the baseline is the same as a ‘no development’ scenario

coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the baseline as well as the additional coal resource development (those that were expected to begin commercial production after December 2012)

in the Galilee subregion there are 17 additional coal resource developments. Seven developments near the central-eastern margin of the subregion had sufficient publicly available information to be assessed in numerical modelling: the open-cut coal mines Alpha and Hyde Park, and the combined open-cut and underground coal mines Carmichael, China First, China Stone, Kevin’s Corner and South Galilee

the remaining 10 coal resource developments in the CRDP are assessed qualitatively in this impact and risk analysis. They comprise the seven non-modelled coal mine projects, from north to south, Clyde Park, Hughenden, Pentland, West Pentland, Milray, Alpha West and Blackall, and the three CSG projects, Glenaras, Gunn and Blue Energy.

The difference in results between the CRDP and baseline is the change that is primarily reported in a bioregional assessment (BA). This change is due to the additional coal resource development. This change is quantified for the seven coal mines included in the hydrological modelling.

The groundwater zone of potential hydrological change is defined as the area with at least a 5% chance of exceeding 0.2 m of drawdown in the near-surface aquifer (i.e. Quaternary alluvium and Cenozoic sediments).

The surface water zone of potential hydrological change includes streams and associated riparian fringes where a change in any one of the eight modelled surface waterhydrological response variables exceeds its specified threshold. The thresholds can be generally described as at least a 5% chance of a 1% or greater change in a flow volume, or a three day or greater change in frequency. The surface water zone encompasses much of the Belyando river basin upstream of Lake Dalrymple (Burdekin Falls Dam).

The zone was used to rule out potential impacts on ecosystems and water-dependent assets within the Galilee assessment extent. Water resources and water-dependent assets outside the zone are very unlikely (less than 5% chance) to be impacted by modelled coal resource developments.

Potential hydrological changes

Groundwater

Drawdown due to modelled additional coal resource development occurs in two distinct coal mining clusters near the central-eastern margin of the Galilee subregion. Results from regional groundwater modelling show drawdown due to additional coal resource development of greater than 0.2 m is very likely (greater than 95% chance) for an area of 2,820 km2. It is very unlikely (less than 5% chance) that more than 13,364 km2 of the near-surface aquifer (i.e. Quaternary alluvium and Cenozoic sediments) will experience drawdowns of this magnitude due to additional coal resource development. Groundwater drawdown and impacts on ecosystems or assets are not reported inside a 986 km2 ‘mine exclusion zone’ close to proposed open-cut and underground mines because of very steep hydraulic gradients at the mining operations.

Results for 2 m and 5 m drawdown extents in the near-surface aquifer suggest it is:

very likely that an area of at least 1596 km2 exceeds 2 m of drawdown and very unlikely that more than 4426 km2 exceeds 2 m of drawdown

very likely that an area of at least 1029 km2 exceeds 5 m of drawdown and very unlikely that more than 2711 km2 exceeds 5 m of drawdown.

Modelled drawdowns are also reported for the two deeper confined aquifer systems of the Clematis Group and upper Permian coal measures, both part of the hydrostratigraphic sequence of the Galilee Basin. The pattern and extent of drawdown in these deeper layers differs from that in the near-surface sediment layer, occurring westwards of the mining areas and extending much further towards the central parts of the Galilee Basin. Drawdowns in these deeper layers are important for assessing impacts on some springs and groundwater economic assets (bores).

A relatively low resolution, regional-scale hydrogeological conceptualisation underpins the drawdown predictions from the analytic element model (AEM). Although the hydrogeological conceptualisation used in the AEM is generally well suited for the type of regional, cumulative impact analysis undertaken for this BA, it can lead to overestimated drawdown predictions at some locations within the zone of potential hydrological change. For example, upland areas to the west of the mines lack the uppermost Quaternary alluvium and Cenozoic sediment layer (i.e. Triassic rock units outcrop), which is an important component of the original AEM conceptualisation and affects drawdown predictions in the underlying Clematis Group aquifer. To better understand the likely range of modelled drawdown predictions in areas where the original conceptualisation is not appropriate due to local hydrogeological conditions (e.g. at some spring locations west of the mines), an alternative conceptualisation was also evaluated using the AEM. An important difference between the two AEM conceptualisations is that drawdown from the mines does not propagate via the uppermost (Cenozoic sediment) layer using the alternative approach. For the ‘Springs’ landscape group, the results from these two AEM conceptualisations are compared to better understand the range of potential groundwater responses to the additional coal resource development.

In total there are 6285 km of streams within the zone of potential hydrological change, with impacts to about 25% of this stream length not included in the modelled surface water network (i.e. some potential stream impacts were not able to be quantified).

Zero-flow days

A zero-flow days in the BA for the Galilee subregion is one when streamflow is less than 1 ML/day from the simulated 90-year period (2013 to 2102) for that stream. The most substantial modelled surface water changes are for increases in zero-flow days, and these mostly affect the main channel of the Belyando River, and the Suttor River downstream of its junction with the Belyando River. An approximate 250 km stretch of this river network from downstream of the Native Companion Creek junction northwards to Lake Dalrymple (Burdekin Falls Dam), is very likely (greater than 95% chance) to experience substantial increases in the number of zero-flow days per year. These results indicate that increases in zero-flow days can aggregate from individual mines and result in cumulative impacts that extend beyond individual mine leases along the main Belyando River channel. Other smaller streams that may experience substantial increases in the number of zero-flow days are proximal to the South Galilee, China First, Alpha and Kevin’s Corner mines in the southern mining cluster. North Creek is the main stream likely to experience increases in zero-flow days in the Carmichael, China Stone and Hyde Park northern mining cluster.

Much of the Belyando and Suttor rivers that have a 5% chance of an additional 200 (or more) zero-flow days do not actually flow for 200 days in most years. This apparent anomalous increase in zero-flow days occurs because, in particularly wet years, modelling indicates that the rivers can flow for 200 (or more) days per year. As BAs report the maximum change in zero-flow days due to additional coal resource development, the reporting is biased towards wetter years when these maximum changes can occur.

When comparing these results to interannual variability there is a 50% chance that modelled changes are comparable around the northern mining cluster in the northern-most stretches of the Belyando River upstream of Lake Dalrymple. There is a less than 5% chance that modelled changes of increases in zero-flow days exceed interannual variability for much of the Belyando River around the northern mining cluster.

High-flow days

Changes to high-flow days due to the seven modelled coal mines are generally less substantial, and also tend to have a greater effect on the smaller tributary network within the zone, rather than the main river channels of the Belyando and Suttor. For example, the largest decreases in high-flow days per year occur on Tallarenha Creek, Lagoon Creek and Sandy Creek in the south, due to their proximity to the southern mining cluster. In the north, the main impacts are modelled for North Creek and Bully Creek. Unlike for zero-flow days, these high-flow changes do not accumulate downstream in the Belyando River, such that the Suttor River downstream of the Belyando junction is very unlikely to experience decreases in high-flow days of more than 10 days per year.

The regional-scale modelling shows that at most nodes the maximum change is relatively small compared to interannual variability, although there is a less than 5% chance that some nodes will experience changes comparable to interannual variability.

Annual flow

Decreases in annual flow volumes are very consistent across all reported percentiles. These reductions typically range from 5% to 20%, and affect the same tributary streams that are expected to experience reductions in high-flow days. There is only one model node, on Tallarenha Creek downstream of the proposed South Galilee Coal Mine, where reductions in annual flow volume may locally exceed 20%.

There is a less than 5% chance for the various surface water nodes that occur on Sandy Creek, North Creek and Bully Creek that the modelled annual flow changes may be considered comparable to or greater than interannual variability.

Water quality

Any change in hydrology could result in changes in groundwater and/or stream water quality; however, this was not modelled as part of the BA. A range of regulatory requirements are in place in Queensland that are intended to minimise potential water quality impacts from coal resource development.

Impacts on, and risks to, landscape classes

The impact and risk analysis investigates how hydrological changes due to additional coal resource development may affect ecosystems at a landscape scale. Estimates of overall ecosystem risk integrate understanding from the conceptual model of causal pathways, hydrological modelling and expert opinion. The strength of this approach is that it provides a measure of the relative risk and emphasises where attention should focus, and also where it should not.

The diverse natural and human-modified ecosystems in the Galilee assessment extent were classified into 31 landscape classes, which were aggregated into 11 landscape groups based on their likely response to hydrological change. Landscapes that are outside of the zone of potential hydrological change are very unlikely (less than 5% chance) to be impacted and include more than 100,000 km2 of groundwater-dependent vegetation; 387,000 km of streams; 20,000 km2 of wetlands; and 1,359 springs in the assessment extent. Receptor impact modelling was undertaken for five of the 11 landscape groups in the Galilee assessment extent.

‘Springs’ landscape group

Groundwater flow from springs supports endemic flora and fauna, the building of peat mounds and associated groundwater-dependent vegetation. There are three clusters of springs within the zone of potential hydrological change: the Doongmabulla Springs complex, Permian springs cluster and the Triassic springs cluster. Springs are not represented directly in the hydrological model, and drawdown is estimated by comparing model layer drawdown (for the source aquifer) at the known location of the springs. It is likely that drawdown estimates based on the original analytic element model (AEM) conceptualisation overestimate drawdown in some areas where the actual distribution and thickness of the uppermost aquifer layer is much more restricted than what is implemented in the original AEM. To account for such locally overestimated drawdown values, an alternative conceptualisation was developed and used to investigate drawdown in areas where the uppermost aquifer (Quaternary alluvium and Cenozoic sediment) does not exist as an extensive, sheet-like layer that is in direct (and hydraulically unimpeded) connection with the mining areas. These areas mainly occur to the west of the mines where the Triassic rock units of the Galilee Basin outcrop, and include the area of the Doongmabulla Springs complex. Potential ecosystemimpacts for the springs were investigated using a qualitative mathematical model to evaluate ecological relationships within aquatic communities.

The Doongmabulla Springs complex includes 187 springs associated with the Carmichael River and its tributaries. The hydrogeological evidence suggests that the Clematis Group aquifers, rather than the deeper Permian aquifers, are the primary source aquifers for these springs. The original AEM conceptualisation predicts that drawdown due to additional coal resource development is very likely toexceed 0.2 m in the source aquifer of 181 of the 187 springs in this complex. However, estimates using the alternative conceptualisation indicate that no springs in the Doongmabulla Springs complex are predicted to experience median additional drawdown in excess of 0.2 m. Resultant changes due to pressure reductions for the Doongmabulla Springs complex may include changes in water flows and decrease in water availability to groundwater-dependent ecosystems (GDEs), although the long-term impact on the springs and spring wetlands and related organisms is unclear or contestable.

In the Permian springs cluster, it is very likely that at least 5 springs and very unlikelythat more than 7 springs will experience drawdown in excess of 5 m in the upper Permian coal measures due to additional coal resource development. Resultant changes due to pressure reductions for the Permian springs cluster may include reduction in flows at the surface for all springs within the Mellaluka Springs complex, with large hydrological changes that will potentially result in the loss of ecological functioning of these springs.

Drawdown for the 12 springs in the Triassic springs cluster cannot be reliably estimated by the AEM, but results are likely to fall within the range predicted for the Clematis Group model layer.

None of the other 1353 Great Artesian Basin (GAB) springs identified in the Galilee assessment extent are in the zone of potential hydrological change.

The remaining streams in the zone of potential hydrological change are not groundwater dependent (3484 km) and so are unlikely to be affected by groundwater drawdown. This includes most of the minor temporary streams (1028 km) in the zone of potential hydrological change that are potentially impacted but not represented in the surface water model. Potential hydrological changes include increased low-flow days and low-flow spells along up to 177 km of temporary streams in the zone. The impact analysis indicates that high-flow environments in some minor stream segments are ‘at some risk of ecological and hydrological changes’, mainly in downstream parts of the Belyando and Suttor rivers above Lake Dalrymple (see section 3.4.5.3).

‘Floodplain, terrestrial GDE’ landscape group

Most groundwater-dependent vegetation in the zone of potential hydrological change occurs on floodplains (2433 km2 or about 64% of groundwater-dependent vegetation in the zone). It is very unlikely that more than 296 km2 of groundwater-dependent vegetation on floodplains experiences more than 5 m of drawdown due to additional coal resource development. Over half of the groundwater-dependent vegetation in the zone is located on floodplains intersected by temporary streams that are potentially impacted but not represented in the surface water model. Potential hydrological changes include decreased overbank flows that may affect up to 355 km2 of floodplain vegetation. Expert-derived estimates of antecedent foliage cover, additional drawdown and decreased overbank floods indicate up to 3% of floodplain, terrestrial GDEs in the zone (where quantifiable) are ‘at some risk of ecological and hydrological changes’ (see Section 3.4.6.3). This includes floodplain areas along Alpha, North, Sandy and Tallarenha creeks, and the Belyando and Carmichael rivers.

Of the 241 ecological assets in the zone, 148 are identified as being ‘more at risk of hydrological changes’ because all or part of the area where these assets occur is within one or more of the potentially impacted landscape groups and there is a greater than 50% chance of the modelled hydrological change exceeding the defined threshold (see Section 3.5.2.1). These assets include:

A concentration of ecological assets occurs in the ‘Springs’ landscape group. Although the 200 springs in this landscape group occupy less than 1% of the zone of potential hydrological change, 48 ecological assets (20% of all ecological assets in the zone) intersect with it, including 16 that are confined entirely to the zone. Doongmabulla Springs complex is the location where most of these assets occur, and they include the springs themselves, the Doongmabulla Mound Springs Nature Refuge, habitat (potential species distribution) of an EPBC Act-listed threatened ecological community, ‘The community of native species dependent on natural discharge of groundwater from the Great Artesian Basin’, and habitat (potential species distribution) of two EPBC Act-listed threatened plant species (blue devil (Eryngium fontanum) and salt pipewort (Eriocaulon carsonii)).

Economic assets

There are 129 economic water-dependent assets within the Galilee assessment extent, all of which are classed as either water access rights or basic water rights (stock and domestic). Of these, 96 are associated with groundwater management areas and 33 with surface water management areas. Each asset consists of a variable number of asset ‘elements’, which are typically individual groundwaterbores or surface waterextraction points.

The hydrological changes due to the seven coal mines modelled for the BA of the Galilee subregion will potentially impact six of these economic water-dependent assets, comprising five groundwater assets and one surface water asset. The surface water asset is a basic water right under the Water Plan (Burdekin Basin) 2007.

Three of the groundwater economic assets potentially impacted due to additional coal resource development are associated with the Clematis Group aquifer, and are managed as part of the Water Plan (Great Artesian Basin) 2006 (although this plan was superseded in September 2017). Of the bores that source water from the Clematis Group aquifer near Jericho, the maximum amount of drawdown is less than 1 m for all modelling results. Potential impacts for many of the bores near Alpha cannot be quantified due to limitations of the groundwater modelling approach, and thus remain a key knowledge gap.

There are about 105 bores within the zone of potential hydrological change that are interpreted to source water from the near-surface unconfined aquifer (Quaternary alluvium and other Cenozoic sediments) that were not listed as a BA economic asset (see Section 3.5.3.4). However, 35 of these are either in the ‘mine exclusion zone’, company owned or ‘abandoned or destroyed’. Of the remaining bores analysed, it is very likely that seven will experience at least 0.2 m of drawdown, and very unlikely that more than 52 bores will be affected by this level of drawdown. Drawdowns of greater than 2 m are modelled to affect between 2 and 13 bores (at the 5th and 95th percentiles respectively).

A further 31 bores in the central-eastern Galilee subregion source water from the Clematis Group aquifer but are not in the water-dependent asset register. The maximum modelled drawdown is about 1 m and well below the 5 m threshold legislated in Queensland for ‘make good’ provisions for consolidated rock aquifers. There are also 34 non-company bores within the zone that tap the upper Permian coal measures, the main coal mining (and dewatering) target in the Galilee Basin. Based on results from the AEM for the Galilee subregion most of these Permian-sourced bores are predicted to experience drawdowns in excess of 20 m.

Sociocultural assets

Of the 151 sociocultural assets in the Galilee assessment extent, only four partially intersect with the zone of potential hydrological change. Three of these assets were nominated from the Register of the National Estate, including Doongmabulla Springs (natural indicative place), Lake Buchanan and catchment (natural registered place), and the Old Bowen Downs Road (historic indicative place). Consultation with several local Aboriginal groups in the Galilee subregion identified 24 species of fauna and flora that are of critical cultural heritage value, all of which may be water dependent. However, as there was no spatial information associated with these Indigenous assets it was not possible to determine if they occur within the zone of potential hydrological change.

Future monitoring

Post-assessment monitoring is important to test and validate (or not) the risk predictions of the assessment. At the highest level, monitoring effort should reflect the risk predictions, and focus the effort where the changes are expected to be the largest (i.e. areas concentrated around main proposed coal resource developments). However, it is important to place some monitoring effort at locations with lower risk predictions to confirm the range of potential impacts and identify unexpected outcomes.

Future surface water monitoring should focus on streams that pass near the additional coal resource developments, where the predicted changes suggest adverse effects on subregion assets. These streams include: Native Companion, North, Sandy, Alpha and Tallarenha creeks, and the Belyando and Carmichael rivers.

Future groundwater monitoring could focus on confined parts of Clematis Group aquifer and Dunda beds, in particular, up-hydraulic gradient (west and south) of the Doongmabulla Springs complex. Monitoring of Cenozoic aquifers in key areas of the Belyando River floodplain (e.g. near Alpha) would assist in better understanding the degree of drawdown in the near-surface aquifer and the potential connectivity and flux with deeper aquifers.

Gaps and opportunities

The BA for the Galilee subregion has been undertaken using the best available information within the constraints and timing of the Bioregional Assessment Programme. The Assessment focuses on regional-scale cumulative impacts of coal resource development, and provides an important framework for future environmental impact assessments of new coal mines or CSG developments and the local geological, hydrogeological and hydrological modelling and analyses that support them. There are also opportunities to tailor the BA modelling results, for example:

to consider alternative CRDP futures with a different selection of mining and CSG developments

to further refine the Galilee Basin hydrogeological (GBH) model to better understand water balance and fluxes between different aquifer systems, for testing different CRDPs and for future management of water resources in the Galilee subregion.

There are also specific opportunities for further improvement to follow on from the work completed for this BA. This is of particular importance for the greenfield Galilee subregion where there is no history, data or information for baseline coal resource development (see Section 3.7.4).